1. Field of the Invention
This invention relates generally to a nuclear fuel rod spacer assembly.
2. Description of Related Art
During manufacture and subsequent installation and repair of components comprising a nuclear reactor coolant circulation system, diligent effort is made to assure removal of all debris (e.g., metal chips and shavings, small solid sections of metal, and the like) from the reactor vessel and its associated systems which circulate coolant therethrough under various operating conditions. Although elaborate procedures are carried out to help assure debris removal, and in spite of the safeguards used to effect such removal, some chips and metal particles still remain hidden in the system.
For example, damage to the fuel assembly may occur due to debris trapped at the fuel rod spacer assembly in reactors. The damage consists of fuel rod tube perforations caused by fretting of debris in contact with the exterior of the tube. The debris tends to be relatively thin rectangular pieces, as opposed to pieces which are spherical in shape. Specifically, most of the debris consists of metal turnings which were probably left in the primary system after steam generator repair or replacement. The debris may lodge in the region of within the spaces between its “egg-crate” shaped cell walls (or ferrule cells) and/or the leading edge of the fuel rod spacer assembly.
One approach to solve the above problem has been to install filtering devices into a lower tieplate of the bundle for catching the debris and remove the filters during preoperational testing. Although these filtering devices have been effective in filtering out a wide range of debris types and sizes, these conventional filters do not filter all the debris and do not protect debris from entering the fuel bundle, for example, from the top of the bundle
While the conventional approach may operate reasonably well and may generally achieve their objectives under the range of operating conditions for which they were designed, they also create several other problems (e.g., compatibility issue, inconsistent operating cycle, cost, and others.). Consequently, a need exists for a fresh approach to the problem of debris capture in nuclear reactors. The new approach must be compatible with the existing structure and operation of the components of the reactor, be effective throughout the operating cycle of the reactor, and at least provides overall benefits which outweigh the costs it adds to the reactor.